The present invention relates to a process chamber and process monitoring window.
In integrated circuit fabrication, layers of semiconductor, dielectric, and conductor materials, such as for example, polysilicon, silicon dioxide, aluminum and copper layers are deposited on a substrate and subsequently processed, for example, by etching with an etchant plasma, to form active devices. The layers are deposited on the substrate in a process chamber by processes such as chemical vapor deposition (CVD), physical vapor deposition (PVD), thermal oxidation, ion implantation and ion diffusion. After deposition, a resist layer of photoresist or hard mask is applied on the deposited layer and patterned by photolithography. Portions of the deposited layers lying between the resist features are etched using RF or microwave energized halogen and other reactive gases to form etched features.
In these fabrication processes, it is often desirable to monitor in-situ the process being performed on the substrate by a process monitoring system. For example, in CVD and PVD processes, it is desirable to stop the deposition process after a desired thickness of a layer is deposited. In etching processes, endpoint detection methods are used to prevent overetching of layers that are being etched. Typical process monitoring methods, include for example, plasma emission analysis, ellipsometry, and interferometry. In plasma emission analysis, an emission spectra of a plasma is measured to determine a change in chemical composition that corresponds to a change in the layer being processed, as for example, taught in U.S. Pat. No. 4,328,068 which is incorporated herein by reference. In ellipsometry, a polarized light beam is reflected off a layer on the substrate and analyzed to determine a phase shift and a change in magnitude of the reflected light that occurs with changes in the thickness of the layer, as for example disclosed in U.S. Pat. Nos. 3,874,797 and 3,824,017, both of which are incorporated herein by reference. In interferometry, a non-polarized light beam is reflected off the layer and analyzed to determine a change in magnitude of the reflected light that occurs due to interference of reflected light components from the top and bottom surfaces of the layer on the substrate, as for example, described in U.S. Pat. No. 4,953,982, issued Sep. 4, 1990, which is incorporated herein by reference. These process monitoring methods require a high strength optical transmission signal through the window and also require viewing or signal sampling of relatively large surface area of the substrate.
A typical process monitoring system comprises an optical sensor system for detecting and measuring light emissions or light reflections through a window in a wall of the process chamber. The window is transparent to particular light wavelengths to allow light to be transmitted in and out of the chamber while maintaining a vacuum seal with the chamber. When monitoring a layer on a substrate, the transparent window is positioned in the chamber wall in direct line of sight of the substrate. Process monitoring windows are typically constructed from quartz which is resistant to high temperatures and are sealed to the chamber surface with O-ring seals positioned along their edges.
However, in many deposition and etching processes, a thin cloudy film of residue deposits and byproducts are deposited on the process monitoring window as substrates are being processed in the chamber. The process residues are deposited on the window at rates often in excess of 1 micron in 25 to 50 hours of process operation. The deposited film of process residue changes the properties or intensity of the light transmissions passing through the window. For example, in plasma emission analysis, the residue deposits selectively filter out particular wavelengths of light from the optical emission spectra of the plasma resulting in errors in process monitoring measurements. In ellipsometry, the residue deposits change the state of polarization of the light beam transmitted or reflected through the window causing erroneous ellipsometric measurements. As another example, in interferometry, the deposits absorb and lower the intensity of the light passing through the window resulting in a lower signal-to-noise ratio.
To avoid these problems, conventional processing monitoring windows are periodically replaced or cleaned to remove the residue deposits formed on the windows. For example, in typical etching processes, after etching a certain number of wafers, or operating cumulatively for about 10 hours, the chamber is opened to the atmosphere and cleaned in a xe2x80x9cwet-cleaningxe2x80x9d process, in which an operator uses an acid or solvent to scrub off and dissolve the deposits accumulated on the window and chamber walls. After cleaning, the chamber is pumped down for 2 to 3 hours to outgas volatile acid or solvent species, and a series of etching runs are performed on dummy wafers. In the competitive semiconductor industry, the downtime of the chamber during such cleaning processes can substantially reduce process throughput and increase processing costs per substrate. Also, manually performed wet cleaning processes are often hazardous, and the quality of cleaning varies from one session to another.
One approach to solving the residue deposition problem uses a recessed window positioned in a long tube that opens into the chamber. Because the process gas or plasma in the chamber has to travel though the length of the tube before reaching the recessed window, the deposition of process residues on the surface of the recessed window inside the tube is markedly reduced. However, the high aspect ratio (length/diameter) of the elongated tube makes it difficult to monitor a sufficiently large sampling area inside the chamber, and reduces the total light flux. This limits the accuracy of the process monitoring systems during processing of a batch of substrates or sometimes even for a single substrate. In addition, the elongated tube takes up a large amount of space outside the chamber, which is undesirable in tight clean room spaces, and the tube is also difficult to fit in-between other components of the process chamber.
In another solution, the process monitoring window is selectively heated to prevent deposition of process residue deposits, as described in commonly assigned U.S. Pat. No. 5,129,994, to Ebbing et al., issued on Jul. 14, 1992. However, while suitable for certain types of processes, heating does not prevent all forms of residues from condensing and depositing on the window, and in certain processes, heating can actually increase the rate of deposition of process residue on the window.
In yet another approach, photosensitive equipment is used to sample signals of the light emissions or reflections from the chamber/substrate and mathematically manipulate the sampled data to increase the signal to noise ratio of the light signal passing through a cloudy window, as for example, described in U.S. Pat. No. 5,738,756 to Liu, issued on Apr. 14, 1998. However, complex mathematical manipulations can delay process response times. In etching processes, even a small time delay can result in undesirable charging or lattice damage of the underlying layers, especially for underlying polysilicon layers. In addition, these processes are not always able to increase the signal to noise ratio by a sufficient amount to provide a discernible signal. If the signal is too small, the fabrication process may never be terminated, and if it is too large, the process may be prematurely terminated.
The process residues deposited on windows are a particular problem when monitoring etching processes in which etching of a thick overlayer has to be stopped before etching through a relatively thin underlayer. For example, the aggressive halogen containing gases etchant gases that are used to etch a relatively thick layer will often uncontrollably etch through or damage any thin underlayers, without an accurate and reliable process monitoring system. This is especially a problem when etching a polysilicon overlayer to expose a thin gate oxide underlayer. After the polysilicon etching process, it is desirable for the remaining thickness of the gate oxide layer to be very close to a nominal and predetermined thickness. As the gate oxide layer becomes thinner, it is more difficult to accurately etch through the polysilicon overlayer without overetching into the gate oxide layer. It is further desirable to stop the etching process on the gate oxide layer without causing charge or lattice damage to underlying silicon by exposed the silicon to the energetic etchant plasma. This type of process control is only possible with a reliable and consistently performing process monitoring system.
Thus it is desirable to have a chamber and process monitoring system that allows monitoring of processing of substrates in the chamber, without excessive signal loss during continued processing of the substrate. It is further desirable to have a process monitoring window that prevents or reduces deposition of process residue on its surfaces and exhibits a low rate of erosion in reactive halogen gases and plasmas. It is also desirable to have a method of monitoring processing of a substrate that provides accurate and repeatable processing results, especially for etching thick overlayers on thin underlayers.
The present invention provides a process chamber for processing a substrate and monitoring the process being conducted on the substrate with a high degree of accuracy and repeatability. The chamber comprises a support, a process gas distributor, and an exhaust system. The chamber has a wall comprising a window that allows light to be transmitted therethrough. The window comprises a transparent plate covered by a mask having at least one aperture extending through the mask so that light can be transmitted through the aperture of the mask and the transparent plate to monitor the process being conducted on the substrate. The mask covering the transparent plate reduces deposition of process gas byproducts and other deposits on the window during a process in which a substrate is held on the support and processed by process gas that is distributed by the gas distributor and is exhausted by the exhaust system.
In another aspect, the present invention comprises a process chamber comprising a support having a receiving surface that is adapted to support a substrate. A gas distributor provides process gas in the process chamber to process the substrate and form process gas byproducts. First means are provided for transmitting light into and from the process chamber during processing of a substrate in the process chamber. Second means are provided for masking the first means to reduce deposition of process gas byproducts formed in the process chamber. An exhaust comprising pumps exhaust the process gas and process gas byproducts from the process chamber.
In yet another aspect, the present invention comprises a method of processing a substrate, comprising the steps of placing the substrate in a process zone and maintaining first process conditions in the process chamber to process the substrate, the first process conditions including providing an energized process gas to the process zone. An incident light beam is directed through a window adjacent to the process zone to be incident on the substrate. A measurable intensity of the reflected light beam passing through the window is measured by holding a mask having apertures against the window to reduce deposition of process gas byproducts on the window. A property of a reflected light beam that is reflected from the substrate is measured. The first process conditions are changed to second process conditions in relation to the measurement of the property of the reflected light beam.
In another aspect, the present invention comprises a method of etching a layer on a substrate substantially without etching or damaging an underlayer. The method comprises the steps of placing the substrate in a process zone and maintaining process conditions in the process zone to etch a layer on the substrate and form process gas byproducts, the process conditions comprising one or more of process gas composition and flow rates, power levels of process gas energizers, process gas pressure, and substrate temperature. An etching endpoint is detected immediately prior to etching through the layer on the substrate by the steps of (1) directing an incident light beam through a window adjacent to the process zone to be incident on the substrate, (2) maintaining a measurable intensity of the reflected light beam through the window by holding a mask having apertures against the window to reduce deposition of process gas byproducts on the window, and (3) measuring a property of a reflected light beam that is reflected from the substrate immediately prior to etching through the layer on the substrate. The process conditions in the chamber are changed in relation to the measurement of the property of the reflected light beam.
In another aspect, the invention is directed to a process chamber having a window in a wall of the process chamber for monitoring the process being conducted on a substrate and a magnetic field source adapted to provide a magnetic flux across the window. The chamber comprises a support, a process gas distributor, and an exhaust system by which a substrate held on the support is processed by the energized process gas, forming process residues in the process chamber, and the magnetic field source provides magnetic flux across the window to reduce the deposition of process residues on the window.
In yet another aspect, the present invention comprises a process chamber for processing a semiconductor substrate, the process chamber comprising a window and means for maintaining a magnetic flux across the window. The process chamber further comprises a support, a process gas distributor, and an exhaust system. A substrate held on the support is processed by the energized process gas thereby forming process residues in the process chamber. The means for maintaining magnetic flux across the window reduces deposition of process residues on the window.
The present invention also comprises a method of processing a substrate, comprising the steps of placing the substrate in a process chamber and maintaining first process conditions in the process chamber to process the substrate, the first process conditions including providing an energized process gas to the process chamber. Maintaining a magnetic flux across a window in a wall of the process chamber. Directing an incident light beam through the window, and changing the first process conditions are changed to second process conditions in relation to the measurement of the property of the reflected light beam.
In another aspect, the invention is directed to a process chamber having a window in a wall of the process chamber for monitoring the process being conducted on a substrate, and an electrical field source adapted to couple electrical energy to the window. The chamber further comprises a support, a process gas distributor, and an exhaust system. By which a substrate held on the support is processed by the energized process gas, forming process residues in the process chamber, and the electrical energy coupled to the window reduces deposition of the process residues on the window.
In yet another aspect, the present invention comprises a process chamber for processing a semiconductor substrate, the process chamber comprising a window, and means for electrically biasing the window. The process chamber further comprises a support, a process gas distributor, and an exhaust system. By which a substrate held on the support is processed by the energized process gas, forming process residues in the process chamber, and the means for electrically biasing the window reduces deposition of process residues on the window.
In yet another aspect, the present invention comprises a method of processing a substrate, comprising the steps of placing the substrate in a process chamber and maintaining process conditions in the process chamber to process the substrate, the process conditions including providing an energized process gas in the process chamber. Providing a window in a wall of the process chamber, and maintaining an electrical flux across the surface of the window. The electrical flux having an electrical field component that is perpendicular to the plane of the window.